Daron Ferris, MD, from Georgia Regents University in Augusta, and colleagues examined the long-term safety, immunogenicity, and effectiveness of HPV4 vaccine in a cohort of 1,781 sexually-naive 9–15-year-olds. Participants were randomized in a 2:1 ratio to receive HPV4 vaccine or saline at day one and months two, four, and six. At month 30, the 482 participants in the placebo group also received HPV4 vaccine.

The researchers found that vaccination-induced anti-HPV response persisted through 96 months for each of the HPV4 vaccine types. None of the 429 subjects who received HPV4 vaccine at a mean age of 12 developed HPV6/11/16/18-related disease or persistent infection. Among those aged ≥16 years, acquisition of new sexual partners was about one per year. The baseline rate of seropositivity to one or more of the four HPV types was similar for those receiving the vaccine at month 30 and for those vaccinated at day one (1.9 vs. 1.7%). Four of nine individuals vaccinated at the later age were seropositive to three vaccine types.